310 G. H. PARKER 



muscle contracts much more quickly than the circular muscle 

 does and its activity, unlike that of the circular muscle, is quite 

 abolished by such drugs as chloretone. These features are the 

 characteristics of a muscle under nervous control as contrasted 

 with one brought into action by direct stimulation, and I, there- 

 fore, conclude that the longitudinal muscle of the stalk is nor- 

 mally under nervous influence, and that the circular muscle is 

 stimulated directly. 



Under such circumstances the interplay between the longi- 

 tudinal and circular muscles in the shortening and elongation 

 of the stalk as a result of stimulation is easily pictured. Any 

 normal stimulus applied to the stalk gives rise to the impulses 

 that spread through the ectodermic nerve-net and call forth 

 an immediate contraction of the longitudinal muscle. As a 

 result the stalk shortens nearly one-half and the axial cells 

 become crowded together causing it to thicken proportionally. 

 In consequence of this thickening the circular muscle is stretched, 

 its tonus is probably increased, and it is gradually excited 

 to action, so that on the relaxation of the longitudinal muscle 

 the circular muscle contracts and forces the axial cells back to 

 their original form, thus elongating the stalk. In this way 

 the two muscles are brought into harmonious action though only 

 one of them is under nervous control. 



The longitudinal and circular muscles of the proboscis are 

 probably organized upon much the same plan as those of the 

 stalk, but the proboscis is too small an organ to allow of ex- 

 perimental tests such as have been used with the stalk. Its 

 rapid shortening from a long, narrow organ to an almost spher- 

 ical one (Torrey, '04 a, p. 397) and its slow recovery to the 

 elongated form together with the loss of these activities under 

 chloretone treatment all point to a condition essentially similar 

 to that of the stalk. 



In one respect only is there an observable difference be- 

 tween the musculature of the stalk and that of the proboscis. 

 Occasionally the proboscis exhibits spontaneous peristaltic 

 movements. These begin near the distal end of this organ as 

 ring-like constrictions that progress toward its proximal end. 



